your country is beautiful. i went there for the first time last winter and it was amazing !!!!!
porto >>> lisbon
Portugal was my favorite place when i went to Europe (Went to Barcelona in Spain, and Paris in France).
In Portugal had more time because i knew people there, so i was able to know Porto and Lisbon of course, but what i really loved was Leiria and places like Obidos, Alcobaza, Tomar. All that "central" zone was amazing (especially if you like historical and medieval stuff).
That's a difficult one, i would leave that answer to the locals or to those who know more places.
I've been told only amazing things about the north, "close" to Porto (Braga, Guimaraes) but i didn't go there.
Maybe choose by price or your travel expectations (i'm an unc so i liked what our friends living there offered us: historical and beautiful places)